In the art of papermaking, an aqueous suspension containing cellulosic fibres, and optional fillers and additives, is fed through pumps, screens and cleaners, which subject the stock to high shear forces, into a headbox which ejects the suspension onto a forming wire. Water is drained from the suspension through the forming wire so that a wet web of paper is formed on the wire, and the web is further dewatered and dried in the drying section of the paper machine. Drainage and retention aids are conventionally introduced at different points in the flow of suspension in order to facilitate drainage and increase adsorption of fine particles such as fine fibres, fillers and additives onto the cellulose fibres so that they are retained with the fibres on the wire. Examples of conventionally used drainage and retention aids include organic polymers, inorganic materials, and combinations thereof.
WO 98/56715 discloses aqueous polysilicate microgels, their preparation and use in papermaking and water purification. The polysilicate microgels can contain additional compounds, e.g. polymers containing carboxylic acid and sulphonic acid groups, such as polyacrylic acid.
WO 00/006490 discloses anionic nanocomposites for use as retention and drainage aids is papermaking prepared by adding an anionic polyelectrolyte to a sodium silicate solution and then combining the sodium silicate and polyelectrolyte solution with silicic acid.
U.S. Pat. No. 6,103,065 discloses a method for improving the retention and drainage of papermaking furnish comprising the steps of adding at least one cationic high charge density polymer of molecular weight 100,000 to 2,000,000 to said furnish after the last point of high shear; adding at least one polymer having a molecular weight greater than 2,000,000; and adding a swellable bentonite clay.
WO 01/34910 discloses a process for making paper or paper board in which a cellulosic suspension is flocculated by addition of a substantially water soluble polymer selected from (a) a polysaccharide or (b) a synthetic polymer of intrinsic viscosity at least 4 dl/g and then reflocculated by a subsequent addition of a reflocculating system comprising (i) a siliceous material and (ii) a substantially water soluble anionic polymer. Preferably, the substantially water soluble polymer is mixed into the cellulosic suspension causing flocculation and the flocculated suspension is then sheared, e.g. by passing it through one or more shear stages. The water soluble anionic polymeric reflocculating agent is preferably added late in the process, preferably after the last point of high shear, e.g. subsequent to the centri-screen. The process is claimed to provide improvements in retention and drainage.
WO 02/33171 discloses a process for making paper or paper board in which a cellulosic suspension is flocculated using a flocculating system comprising a siliceous material and organic microparticles which have an unswollen particle diameter of less than 750 nm.
WO 02/101145 discloses an aqueous composition comprising anionic organic polymeric particles and colloidal anionic silica-based particles, the anionic organic polymeric particles being obtainable by polymerising one or more ethylenically unsaturated monomers together with one or more polyfunctional branching agents and/or polyfunctional crosslinking agents. The composition is used as a flocculating agent in dewatering of suspended soils, in the treatment of water, wastewater and waste sludge, and as drainage and retention aid in the production of paper.
It would be advantageous to be able to provide a papermaking process with further improvements in drainage, retention and formation.